How is a specimen prepared for a partial thromboplastin time (PTT) and an activated partial thromboplastin time (aPTT)?

Updated: Jul 30, 2019
  • Author: Muhammad Bader Hammami, MD; Chief Editor: Eric B Staros, MD  more...
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Answer

Answer

Usually, 5 mL of citrated, platelet-poor plasma is prepared from 4.5 mL of peripheral venous blood collected via venipuncture and drawn directly into a blue-top tube that contains 0.5 mL of the anticoagulate sodium citrate at a ratio of 9:1.

Invert the tubegently several times to mix the anticoagulant, but do not agitate it.

After collection, the whole blood sample is centrifuged, and the plasma is removed and placed in another blue-top tube.

The plasma should be stored covered at 4°C. The test should be run within 4 hours of collection.

Keep the specimen cool because a high temperature alters the results.


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